1. Field of the Invention
The present invention relates to a gas barrier laminate film having superior gas barrier performance. More precisely, the present invention relates to a gas barrier laminate film that can be suitably used for various kinds of image display devices, in particular, a gas barrier laminate film useful as a substrate of flexible organic electroluminescence device (henceforth referred to as “organic EL device”), and a method for producing the same, as well as an organic EL device.
2. Description of the Background
Conventionally, gas barrier laminate films prepared by forming a thin film of metal oxide such as aluminum oxide, magnesium oxide or silicon oxide on a surface of a plastic substrate or film have been widely used in packaging of articles which require shielding of various gases such as water vapor and oxygen, and packaging use for preventing deterioration of food, industrial materials, medical supplies and so forth. In addition to the packaging use, gas barrier films are recently coming to be used also in liquid crystal display devices, solar cells, EL devices and so forth.
In the course of development of image display devices such as liquid crystal display devices and EL devices in recent years, transparent base materials for forming these devices are required to satisfy highly sophisticated requirements in addition to suitability for production of lighter and larger devices, for example, they must have long term reliability and higher degree of freedom of the shape, they must enable display on a curved surface, and so forth. As a transparent base material that satisfies such sophisticated requirements, plastic base materials are beginning to be adopted as new base materials as an alternative to conventional glass substrates, which are heavy, readily broken and difficult to be formed with a larger size. Plastics base materials not only satisfy the aforementioned requirements, but also show more favorable productivity compared with glass substrates because a roll-to-roll system can be used for them, and therefore they are more advantageous also in view of cost reduction.
However, film base materials such as transparent plastic films have a drawback that their gas barrier performance is inferior to that of glass base materials. If a base material having poor gas barrier property is used, water vapor and air permeate the material to, for example, degrade liquid crystals in a liquid crystal cell, form display defects and thereby degrade display quality. In order to solve this problem, gas barrier laminate films in which a metal oxide thin film is formed on a film substrate have been developed so far. For example, as gas barrier laminate films used for packaging materials or liquid crystal display devices, those comprising a plastic film on which silicon oxide is vapor-deposited (Japanese Patent Publication (KOKOKU) No. 53-12953) and those comprising a plastic film on which aluminum oxide is vapor-deposited (Japanese Patent Laid-open Publication No. 58-217344) are known. These films have a water vapor barrier property of about 1 g/m2/day represented in terms of permeability.
The gas barrier performance required for plastic film substrates used for recently developed large-sized liquid crystal displays and high precision displays is about 0.1 g/m2/day in terms of water vapor barrier ability. Furthermore, development of organic EL displays, high precision color liquid crystal displays and so forth has recently progressed, and therefore required are transparent base materials usable for these, i.e., having higher barrier performance, in particular, barrier performance of less than 0.1 g/m2/day in terms of water vapor barrier ability, while maintaining transparency. In order to meet such a demand, recently studied is film formation by the sputtering method or CVD method as a means that can be expected to provide higher barrier performance, in which a thin film is formed by using plasma generated by glow discharge under a low pressure condition. Moreover, an organic luminescence device in which a barrier film having an alternate laminate structure of organic layers and inorganic layers is produced by the vacuum deposition method is proposed in U.S. Pat. No. 6,268,695 (page 4, [2-5] to page 5, [4-49]). Furthermore, a technique of using acrylic monomers having a volume shrinkage ratio of less than 10% for an organic layer in order to impart flexibility required for applications in flexible display devices is disclosed in Japanese Patent Laid-open Publication (KOKAI) No. 2003-53881 (page 3, [0006] to page 4, [0008]).
However, gas barrier property and flexibility of these materials are insufficient for use as a flexible organic EL display substrate, and further improvement has been desired.